This invention relates generally to the applications of optical circulators and more particularly concerns a printing device in which an optical circulator is used for laser light modulation and light leveling.
A conventional raster output scanner utilizes a light source, a modulator and a multi-faceted rotating polygon mirror as the scanning element. The light source, which can be a laser source, produces a light beam and sends it to the modulator. The modulator receives pixel information for modulating the light beam. The modulated light beam will be directed onto a rotating polygon. At the strike of the modulated light beam, the rotating polygon reflects the modulated light beam and causes the reflected light beam to revolve about an axis near the center of rotation of the rotating polygon and scan a straight line. This reflected light beam can be utilized to scan a document at the input of an imaging system or can be used to impinge upon a photographic film or a photosensitive medium, such as a xerographic drum at the output of the imaging system.
Conventional modulators utilize acousto-optic modulation techniques. The acousto-optic modulator is fabricated from a crystal substrate, such as Lithium Niobate, and then must have electronics bonded to it. The fabrication of the acousto-optic modulator is complex, time consuming, and expensive with relatively low yields of parts. The acousto-optic modulators require complex drivers using between 25 and 50 components and a large power output to modulate light. Additionally, acousto-optic modulators are light polarization sensitive.
On low end printing devices liquid crystal devices are utilized to manufacture low cost print heads. However, liquid crystal devices not only require complex circuitry drivers but also have inherently long response times which limit the printing resolution to about 300 dots per inch and the throughput to less then 24 pages per minute.
Accordingly, it is the primary aim of the invention to provide a method of modulating a light beam requiring fewer complex parts and not limited to slow printing applications.
Further advantages of the invention will become apparent as the following description proceeds.